The present invention relates to a level warning device, particularly a power-supply-level warning device for the electronic systems employing a battery power source.
The general idea that a battery check circuit can be adopted in the electronic systems employing batteries, such as the electronic-control shutter mechanisms of cameras, for the weak-battery display of light emitting diodes (called LEDs hereinunder) is already known as introduced under the title "A Single-Chip, Al- Bipolar, Camera Control IC" on IEEE International Solid-State Circuit Conference 1977 February issue pages 214-215.
A battery check can be performed by measuring the power supply voltage since the electromotive force of batteries decreases in accordance with the power consumption thereof.
Weak battery warning should be preferably supplied before the electromotive force of batteries comes down to a low level where the normal operation of such an electronic system is affected.
The check level, therefore, should be preferably set to a low level somewhat above the lower limit of the operation power-supply voltage of the electronic system.
Thereby, the electronic system can be prevented from abnormal operation immediately before and after the start of a warning and can be kept in normal operation for the remaining period before battery replacement time when the warning is started for replacing batteries. Therefore, the operation and maintenance of the electronic system can be facilitated.
The electronic system, however, cannot sufficiently be prevented from the abnormal operation owing to power supply voltage by using only the above-mentioned battery check circuit and by only setting the check level thereof as described above.